Abstract: The characteristics of non-reductive thermal ion emission of Cs 2BO 2 + and Cs 2Cl + with graphite load, using four kinds of common ionization filaments Ta, Re, W and Pt having different work function, are compared in this paper. The results show that strong Cs 2BO 2 + and Cs 2Cl + ion beams, meanwhile high-precision isotopic measurement of boron and chlorine can be obtained by using Ta, Re, W and Pt filaments. The temperatures for emitting Cs 2BO 2 + and Cs 2Cl + ions using Ta filament with lower work function are lower and the precisions are higher. This result suggests that the emissions of Cs 2BO 2 + and Cs 2Cl + ions by loading graphite are not relative to the work function of the ionization filament. Ta and Re filaments are more suitable to isotopic measurement of boron and Ta and W filaments are more suitable to isotopic measurement of Chlorine. Meanwhile, the formation of oxidation layer on the surface of filament is favorable to obtain high precision isotope measurement of chlorine.